1. Field of the Invention
The present invention relates to rehabilitation of asphalt paved roads and highways, and more particularly to a cold, in-place asphalt recycling method of rehabilitating roads and highways.
2. Background of the Invention
Cold in-place recycling of structurally sound but unacceptably cracked asphalt pavements has been used for several decades. This method remediates cracks, which would otherwise promote pavement failure, and delays formation of new cracks in recycled pavement and previously applied hot mix overlays, thereby extending life expectancy of the rehabilitated pavement.
In conventional practice using cold, in-place asphalt recycling, one lane of a distressed pavement is milled on the order of three to five inches deep. A small amount of asphalt emulsion or foamed asphalt is mixed with milled pavement particles or reclaimed asphalt pavement, which will herein be referred to as RAP for brevity. The road surface is then paved with the treated RAP and is subsequently compacted. This operation is carried out directly on pavement being remediated, with no application of heat to reclaimed asphalt.
Milling, treatment of RAP, and paving may be performed by known milling equipment 2, as seen in FIG. 3. Milling is performed with rows of teeth 4 mounted on a milling head 6 which is part of the milling equipment 2, as Seen in FIG. 4. Conventional spacing of adjacent rows of teeth 4 is on the order of about six tenths or two thirds of an inch, or about fifteen millimeters. This spacing interval is indicated by the arrow 8.
Although immediate use by traffic may be permitted upon completion of the process, it is preferred to allow curing of the newly remediated pavement to deter rutting and other defects from developing. Municipal authorities usually require a hot mix asphalt overlay to be applied after a curing interval to seal the recycled mix, to improve strength and to oppose intrusion of water into the remediated roadway.
The conventional treatment summarized above has the drawback of requiring the hot mix asphalt overlay. A further undesirable characteristic is that due to layer thickness of the uncompacted asphalt mix, typically on the order of four to seven inches, and due to sizes of reclaimed asphalt particles, which in the prior art are typically one and one half inches, subsequent compaction is difficult even when using relatively heavy rolling equipment. Inadequate compaction leaves pores in the asphalt, which are subject to permeation by water, and air, which will accelerate eventual failure of the pavement. Although the hot mix asphalt overlay provides a seal, which addresses the deficiency of porosity, this seal comes at significant economic cost, potentially more than doubling the cost of remediation. There is also the matter of additional inconvenience to the motoring public as this second construction process causes additional delays and typically causes localized congestion. The project may also require additional paving to make the remediated roadway compatible with intersecting side streets, driveways, and drainage structures due to paving height discrepancies.